The present invention relates to an apparatus for generating a magnetic biasing field for recording in a magneto-optical memory. By magneto-optical memory is meant any medium for magneto-optical recording presenting magnetic anisotropy perpendicular to its surface.
A medium of magneto-optical recording, or a magneto-optical memory, comprises essentially a magnetic layer stable at ambient temperature. To record in this type of memory, the magnetic layer is first magnetized perpendicular to its surface, e g. upwards. Information is recorded by locally inverting the direction of magnetization by heating the zone to be recorded to a temperature above Curie point and simultaneously applying an external magnetic field. When it cools to the ambient temperature, the new direction of magnetization is "frozen". The zone to be recorded is generally heated using a laser beam, while the magnetic field is obtained using a magnetic field generator such as a coil. Therefore, to record information, either the laser beam or the magnetic field generator can be modulated.
The solution consisting in modulating the magnetic field generator has a number of advantages. In fact, there is perfect symmetry between the two directions of magnetization, upwards and downwards, thus there are no second-order harmonics in the re-read signal. It is therefore not necessary to use an erasure cycle before writing. However, modulation of the magnetic field generator requires manipulation of great energy at high frequency, which causes large-scale losses by dissipation.
As a result, the present invention aims to provide a new apparatus for generating a magnetic biasing field for recording in a magneto-optical memory which substantially reduces dissipation losses.
The present invention also aims to provide a new apparatus for generating a magnetic biasing field for recording in a magneto-optical memory of particularly simple construction and usable whatever the modulation code used for the information signals to be recorded.